1. Field of the Invention
The present invention relates to an internal combustion engine with an apparatus for controlling supercharging pressure, more particularly for an internal combustion engine with an apparatus for controlling supercharging pressure able to increase engine performance during engine acceleration and to achieve stable engine output against changes in atmospheric conditions.
2. Description of the Prior Art
In a conventional internal combustion engine provided with a supercharger, pressure in the intake pipe at the outlet of the compressor is controlled so that it does not exceed a limit determined by the thermal durability of engine exhaust parts and engine strength under high-speed and high-load engine operation. In the conventional supercharger engine, the engine includes at the exhaust pipe thereof a bypass conduit which bypasses a turbine of the supercharger. In the bypass conduit, a bypass valve, which is called a "waste gate valve", is arranged. The bypass valve is connected to an actuator having a diaphragm to which the supercharging pressure acts. When the pressure is lower than the predetermined limit, the bypass valve is kept closed. However, when the supercharging pressure exceeds the predetermined limit, the pressure moves the diaphragm against the force of the diaphragm spring, causing the bypass valve to open. As a result, part of the exhaust gas is deflected from the turbine to the bypass conduit. This reduces the work of the compressor and prevents the pressure from increasing above the limit. This enables the pressure at the outlet of the compressor, which is equal to the supercharging pressure during full opening of the throttle valve, to be controlled below the limit determined by the thermal durability of the exhaust system and the engine strength.
In the above-mentioned supercharger system, the predetermined limit of the supercharging pressure is determined in consideration of the prevention of knocking in a steady engine state. It should be noted that the higher the limit, the greater the occurrence of knocking. If knocking takes place, a so-called knocking feedback system operates to delay the ignition timing from a basic timing determined in accordance with combinations of the intake air amount and engine rotational speed memorized in a memory. This enables the ideal ignition timing to be obtained at every supercharge load condition.
The above-mentioned predetermined limit of the supercharging pressure, however, is directed to the steady engine state, not engine acceleration. A rotational speed which would cause knocking during the steady engine state would not cause knocking during engine acceleration, i.e., it is possible to increase the limit of supercharging pressure during engine acceleration condition without generating knocking. In the prior art supercharger internal combustion engine, however, the limit pressure has been fixed to the value determined in consideration of knocking during the steady engine state and could not be changed during engine acceleration. As a result, it has not been possible to take advantage of the potential increase in output.
The conventional system suffers from another drawback in that the output power changes in accordance with the engine atmospheric conditions. In the conventional system, the pressure of the intake air at the outlet of the compressor directly acts onto the actuator as gauge pressure. The absolute intake pressure, however, is lower under high-altitude engine atmospheric conditions. As a result, the valve will open earlier than it should, resulting in lower engine output. Contrary to this, when the atmospheric pressure is high and the atmospheric temperature is low, while the gauge pressure remains the same, the air density rises. This results on a large increase in the engine output, making it necessary to guarantee engine strength under the maximum output at high air density. This, on the one hand, increases the manufacturing cost of the engine due to the excessive quality required and, on the other hand, results in large fluctuation of the engine output during running.